In a mobile communication network, user equipment (UE) usually performs cell reselection in an idle state, in order to reside in a cell with better signals. Before performing the cell reselection, it is necessary for the UE to detect one or more neighboring cells. Conventionally, when the UE is in the idle state, the UE detects a neighboring cell according to frequency bands assigned by the communication system in which the UE operates. That is, the UE monitors the signal quality of the system-assigned frequency bands other than the frequency band corresponding to the cell in which the UE currently resides. When a monitored frequency band continuously has a better signal quality than the cell in which the UE currently resides, the UE switches to the cell corresponding to the frequency bands with better signal quality. In practical applications, for the purpose of optimizing load balance, a dedicated signal is used to instruct the UE to detect the signal quality of only a few dedicated frequency bands.
Typically, there is a valid time duration associated with the dedicated frequency bands. When the dedicated frequency bands are valid, the UE ignores other frequency bands. However, the valid time duration of the dedicated frequency bands is usually long enough that when the UE moves fast, the dedicated frequency bands do not expire even after the UE switches to a new cell. If the unexpired dedicated frequency bands are different from the frequency band(s) of the neighboring cell(s) surrounding the newly switched cell, the UE cannot detect the neighboring cell(s) based on the unexpired dedicated frequency band.